Coating paper



Patented Oct. 29,1929

UNITED. STATES A ENT; O I

DONALD B. BRADNER, or HAMILTON, onro, assIenoB. m CHAMPION conrrnn PAPER conmmz, or nammon, onto, A. coarona'rron; or: on o COATING PAPER No Drawing.

This invention relates to a process for coating paper and has for its object an im proved method of using starch as a binding agent in coatings.

Paper commonly is coated with a mixture of pigment (china clay, satin white or the like) and a water solution of an adhesive or binding agent such as casein, gelatin'e' or so called treated-starch. The mixture is applied to the paper as afairly thin liquid or slurry and the coated paper is then-driedand :calendered. So called treated starch starch which has been subjected'to chemical treatment and the viscosity of a solution of which is less than the viscosity of a solution of untreated starch of thesame concentration. In using treated starch'as-a binding agentin coatings it has been customary to prepare a solution of the starch by cooking it in water. Attempts to use common un treated starch as the binding agent heretofore have not been successful, since solutions of untreated starch give coating mixtures of such low solid content that they are not suitable, or on the other hand of such high viscosity that they cannot be handled successfully by coating machines. However, treated starch coating mixtures are inferior to casein coating mixtures with respect to solid content and viscosity. It is sometimes desirable in coating paper to apply the maximum of solid matter but the coating mixture must not be so viscous as to interfere with the proper functioning of the coating machine. Besides thecoat-ings should be strongly adherent and relatively insoluble in water. Treated starch coatings have the disadvantage that they are relatively very soluble in water.

Treated starch, casein and gclatine, which are commonly used for coating paper, are relatively expensive as compared with ordinary untreated starch and it is therefore an object of my invention to devise a way to use untreated starch as the binder for paper coatings, i. e., to overcome the difficulty incident to the high viscosity of starch solutions and coating mixtures having a suitable solid content.

I have found that by applying the starch Application filed November s, 1926. Serial noljiuaqolf together witli'jthe desir'ed pigment in the form of a slurry with water to the paper and then developing the adhesive properties of the starch upon the paper the desired results may be obtained. As stated above starch has always heretofore b'een'used in coating paper in theform ot' 'solu tions obtained by cookproperties but being of' 'relatively low solid hesivepropertiesot' the starch, i; e., heated or cooked. [By us ng uncooked starch in the 'form ogt-a slurry, coatingmixtures of higher solid content and lower viscosity-than casein coating mixture-s can be obtained. Casein I coatingmixtures and the resulting coatings are highly satisfactory frhm the standpoint of viscosity, 'solid "content and the quality of the coatings and may serve as a standard for comparison." Moreover, the starch coatings s'o produced-are much less. soluble "than coatings produced from treated starch.

Untreated starch is applied for coating paper in accordance with'niy invention by preparing a slurry of the desired viscosity and solid content of starch powder and a pigment in water and applying the mixture to the paper in the usual way, and the starch in the coating is then gelatinized by heating in the presence of water, after which the coated paper is dried and calendered like paper coated with any other material. Any kind of starch may be used, for instance corn starch, potato starch, rice starch or the socalled treated starch. Treated starch, however, is more expensive thanuntreated starch and the coatings formed therefrom are relatively soluble. Untreated corn starch is quite suitable. Also any suitable pigment may be used for instance, china clay or satin white.

In preparing the coating mixtures it is desirable to add a dispersing agent, the quantity and kind of dispersing agent used depending ing the starch,'such solutions having adhesive 80 parts by weight of china clay.

20 parts by weight of raw corn starch: 120 parts by weight of water.

part by weight of'guni arabic.

The gelatinization ofthe starch may be accomplished in any suitable way; the only requirements, so far as l have found, being that it be heated to gelatinizing temperature 'in the presence of sufiicient water or moisture. 1f the paper coated with the slurry of starch and pigment .is dried.- at a temperature below that at'which-.gelat1nizat1on occurs and is then heated-to gelatinizingtemperature a satisfactory result-is not obtained, but if the wet paper with the starchsp igment coating is heat- ;ed to &the ,gelatim'zing.temperaturepf the starchundernon-drying.or not too rapid dr-yjing conditions, a satisfactory-result is ob- ,tained.- The gelatim'z ing temperature of starch varies from 50: to 80" 0., depending .upon the varietyof-starch used. It is the .amtemperature at which starch reacts with waten to formaia gelatinous-mass.- The starch granules-swell and become more or less transparent and at the same time the starch takes. I

on adhesive properties. The preferred method is to contact the wet coated paper with direct steam which preferably is not superheated or only slightly superheated. The time required for the gelatinization of the starch in the coating is very short. The minimum time hasnot been determined but it has been found :that exposure to steam at pra. tically atmostoform a hard sized coating. The steam treatment may be accomplished, for instance, bypassing the wet coated paper through a steam chest.

Waxes and similar materials to improve the finish, color, or calendering qualities of the coatings may be mixed with the starch slurry or applied to the coated paper either before or after drying in the well-known manner without departing from my invention. It is also within the scope of my invention to add to the starch slurry dyes, or other coloring or tinting agents such as, for instance, aniline colors or mineral colors. It is also within the scope of my invention to add softening agents such as glycerine or castor oil. Additional coatings of the starch mixture or of other coating material may be applied to the paper in instance, by treatment with acids.

the known manner. Such additional coatings may be applied to the coated paper either before or after drying but after the starch coating has been heated as described to develop its adhesive properties.

The process of my invention may be used for applying coatings to only one side or to both sides of paper and coatings on both sides of the paper may be applied simultaneously.

Although the coating process of the invention is designed for heavy coating paper, it may, of course, be used for producing light coatings. in coating paper on both sides of the sheet the application of 25 pounds of coating material to 500 square sheets 25 by 38 inches-weighing 50 pounds is regarded'as a moderately heavy coating, 20 pounds of coating material on the same amount of paper is regarded as a light coating and 30 pounds-of coating material is regarded as a very heavy coating. My process may serve to produce all siuh coatings. I

In the appended claims the expression raw starchis employed to -des1gnate-eitherl;the treated or untreated starch in an uncooked or fungelatinized condition. Treated starch, as

previously stated, -is the material produced by sub] ecting raw starch to sucha-chemical treatment that its solutions are of ='less":viscosity than solutions of raw starch- 0f the same concentration. .The chemical treatment-.ma-yfbe accomplished in a. variety of ways, such as :for Although the chemical changes involved are notidetinitely known it is probable that the starch-'undergoes a depolymerization or degrading change.

I claim:

.1. Process of coating paper in the form of a web or sheet which comprises applying thereto an aqueous slurry containing raw starch and contacting the wet coated-paper with steam.

2. Process of coating paper which-comprises coating, the paper in the form of a .web or sheet with-an aqueous slurry containing raw starch and a pigment, subjecting the coated paper to sutlicient heat without substantial drying to gelatinize the starch, and drying and finishing the coated paper.

3. Process of coating paper in the form of a web or sheet which comprises applying thereto .a coating of an aqueous slurry containing raw starch, and heating the coated paper to the gelatinizing temperature of the starch in the presence of suiiicient moisture to effect the gelatinization of the starch.

4. Process of coating paper in the form of a web or sheet which comprisesapplying thereto a coating of an aqueous slurry containing raw starch and a pigment, and'heating the coated paper to the gelatinizing tempcrature of the starch in the presence of sufficient moisture to effect the gelatinizat-ion of the starch. i

5. Process of coating paper in the form of a web or sheet which comprises applying thereto an aqueous slurry containing raw starch and a pigment and contacting the Wet coated paper with steam.

6. Process of coating paper in the form of a web or sheet which comprises applying thereto an aqueous slurry containing raw starch and contacting the Wet coated paper with substantially saturated steam.

7. Process of coating paper in the form of a web or sheet which comprises applying thereto an aqueous slurry containing raw starch and a pigment, and contacting the wet coated paper with substantially saturated steam.

In testimony whereof, I atfix my signature.

DONALD B. BRADNER. 

